1. Field of the Invention
This invention relates to a light beam scanning apparatus using a light beam such as a laser beam, and, in particular, to a light beam scanning apparatus capable of selectively adjusting the scanning width of a light beam.
2. Description of the Prior Art
A light beam scanning apparatus using a light beam such as a laser beam is well known in the art. Typically, such a light beam scanning apparatus is employed in a recording machine, such as printers and electrophotographic copiers, for optically reading an original document or forming a latent image on the surface of a photosensitive member which has been charged uniformly previously, as well known in the art. Such a light beam scanning apparatus is disclosed, for example, in U.S. Pat. No. 4,294,534. This patent discloses a composite mode copier using xerography, and it is provided with three modes of operation: normal copy mode, laser beam write mode and laser beam read mode. In accordance with the teachings of this patent, a scanning system comprised of a laser oscillator, a hologram light deflector, a f.theta. lens, etc. is used to scan across the width of the surface of a photosensitive drum. And, the drum is driven to rotate at a normal speed during scanning operation. Other prior art light beam scanning apparatuses are disclosed, for example, in Japanese Laid Open Patent Publications Nos. 57-82815 and 57-85018, and the apparatuses disclosed in these publications use hologram as a light beam deflector.
Any of these prior art scanning apparatuses is so structured to carry out light beam scanning across a predetermined single scanning width, as determined in light of the maximum width of a transfer medium to be used. Accordingly, even if original documents to be scanned have different widths or use is made of transfer mediums, to which a copy image reproduced on the drum is to be transferred, having different widths, scanning is carried out across the full scanning width at all times. This is disadvantageous, however, because it is, in fact, not necessary to carry out scanning across the full width when use is made of shorter original documents and/or transfer mediums.